The present invention concerns a photosensitive resin composition and a method of forming a resist pattern and, more in particular, it relates to a photosensitive resin composition suitable for formation of an extremely small pattern, for example, in the manufacture of a semiconductor device, and a method of forming a resist pattern using such a photosensitive composition.
That is, the present invention concerns a photosensitive resin composition and method of forming resist image by irradiating ultraviolet light, deep ultraviolet light, X-ray and electron beam (hereinafter collectively referred to as actinic ray in the present specification), thereby forming an acid in an irradiated portion (latent images) and changing the solubility of the irradiated portion to an alkaline developer by an acid-catalyzed reaction to form a predetermined pattern, as well as a method of forming a resist pattern using the photosensitive composition.
In recent years, the requirement of small pattern with successive generation of VLSI circuits has been remarkably progressed. For example, it is required to form a pattern of less than sub-half micronmeter, like in 64 M, and 256 M.DRAM and a photosensitive composition of excellent resolution capability has been demanded.
For preparing a semiconductor integrated circuit, a reduction projecting aligner (stepper) has been used and a pattern of a size smaller than the wavelength of a light used for exposure can be resolved, by improvement in-an exposure tool or resist. However, it has not yet been obtained such a high resolution capability as capable of forming, for example, of 64 M and 256 M.DRAM device.
On the other hand, an exposure method using X-ray or electron-beam can be expected as an exposure method capable of forming a further smaller pattern than the exposure method using light and, in this case, the minimum size of the pattern formed depends on a beam diameter of X-ray or electron beam and high resolution capability can be obtained.
However, throughput in the wafer processing is important for mass production of LSI irrespective of the exposure method used and it is difficult to put a method to practical use if the productivity is low even if it can form a small pattern. For improving the productivity in the wafer processing, it is extremely important not only for the improvement of a projecting exposure device but also for making the sensitivity higher of a resist (photo-sensitive composition) to be used.
As a resist material for attaining an increased sensitivity, chemically amplified photosensitive resin compositions containing a compound showing high reactivity under the presence of an acid catalyst and an acid precursor forming an acid under the irradiation of actinic ray have been disclosed, for example, in U.S. Pat. No. 3,779,778, Japanese Patent Laid-Open No. Sho 59-45439 and Japanese Patent Laid-Open Hei 2-25850. According to the descriptions of the prior art, a compound or polymer having acetal groups, or a compound or polymer having t-butyl groups has been used as a highly reactive medium. The above-mentioned compound contains an acid decomposing group and is denatured into a compound or polymer that changes the solubility to a liquid developer, by the capability of reaction of an acid generated by the irradiation of actinic ray.
However, since the existent resist material described above has a small difference in the dissolving speed to a developer between an irradiated area and a non-irradiated area, it brings about a problem of lowering a so-called .gamma. value (lowering of resolution capability), which is a significant bar upon forming a small pattern at a high accuracy. Further, when an ingredient reacting under the presence of an acid catalyst and an alkali soluble resin are used in admixture, it results in a serious problem of separation into two inhomogeneous layers, or forming an insoluble surface inhibition layer by microphase separation of insoluble surface inhibition layer, thereby deteriorating the shape of a pattern. Further, the chemically amplified resist material also involves a problem in the stability upon treatment such as shelf life (storable period) or stability in processing.
As described above, it has been difficult in the prior art to compatibly provide high sensitivity, high resolution ability and high stability altogether.